1. Field of the Invention
The present invention relates to a semiconductor device and, more particularly, to a semiconductor device having a structure that allows a reduction in the cell size of a vertical bipolar transistor.
2. Related Background Art
FIG. 1 schematically shows an example of the construction of a vertical pnp bipolar transistor.
Referring to FIG. 1, the transistor includes a p-type semiconductor substrate 101, an n.sup.+ -type buried layer 102, p.sup.+ -type buried layers 103a and 103b, an n-type epitaxial layer 104, a p-type isolation region 105a, a p-type collector region 105b, an n-type channel-cut region (channel stopper) 106, a field oxide 107, gate oxide film 108, an n-type base region 109, an n.sup.+ -type base diffusion region 110, a p.sup.+ -type collector electrode 112a, a p.sup.+ -type emitter region 112b, an inter-layer CVD film 113, a collector metal electrode 114a, a base metal electrode 114b, and an emitter metal electrode 114c.
As shown in FIG. 1, the vertical pnp bipolar transistor has the n.sup.+ -type buried layer 102, the p.sup.+ -type buried layer 103b and the p-type collector region 105b, all being subsequently formed on the p-type semiconductor substrate 101 of single-crystal silicon or the like. Also, the n-type epitaxial layer 104 is formed surrounding the p-type collector region 105b. Within the p-type collector region 105b, the p.sup.+ -type emitter region 112b and the n.sup.+ -type base diffusion region 110 are formed. The p.sup.+ -type collector electrode 112a is provided contacting the p-type collector region 105b. On the p.sup.+ -type collector electrode 112a, the p.sup.+ -type emitter region 112b, and the n.sup.+ -type base diffusion region 110, the collector metal electrode 114a, the emitter metal electrode 114c, and the base metal electrode 114b are respectively provided.
Hitherto, the base metal electrode 114b has been provided on the n.sup.+ -type base diffusion region 110 through a contact (not shown) after the formation of the region 110 by implanting ions into the n-type base region 109.
However, in a vertical bipolar transistor having the above-described construction, the margin around the base metal electrode 114b, that is, the respective distances from the n.sup.+ -type base diffusion region 110 to the p.sup.+ -type emitter region 112b and to the p.sup.+ -type collector electrode 112a, is inevitably determined by such factors as the level of precision with which the regions, etc. are aligned with each other during the processes in which they are formed. Thus, a problem arises, and it is difficult to reduce the cell size of a vertical pnp bipolar transistor.
Also, inversion at the surface of the n-type base region 109 may sometimes entail a reliability problem.